Such a device has become known from German Offenlegungsschrift No. DE-OS 41 10 095. This prior-art spectrometer uses a laser diode as the transmitting unit, which is operated with a modulated control current. The modulated laser radiation penetrates a gas cuvette, in which the transmitted radiation is attenuated, with a corresponding superimposition of the radiation wavelength and the absorption wavelength, in proportion to the amount of gas components to be detected in the measuring chamber. To generate a state of inversion, the laser diode is supplied with a constant current, which is modulated at a frequency in the kHz range. Due to this modulation, the laser frequency or wavelength is tunable within a wavelength range of one tenth to a few nanometers (nm), depending on the design of the laser diode. A radiation detector receives the laser radiation passing through the measuring chamber and generates a measured signal as a function of the absorption of the laser radiation in the measuring chamber. The second or higher derivation of the measured signal (derivative spectroscopy) is usually used for the evaluation. The measured signal received is evaluated by an electronic circuit (lock-in amplifier), and it is displayed. In the case of the prior-art spectrometer, it is the concentration of oxygen in the measuring chamber. The prior-art device operates with a laser diode, whose emission radiation is in the range of the red spectrum (760-770 nm).
Many of the gas components to be investigated in a gas mixture absorb especially readily in a narrow-band wavelength range of the ultraviolet range, but this section is poorly accessible to common laser spectroscopy with simple means.
It has been known (J. R. Murray: Laser Spectroscopy and its Applications, New York, 1987) that tunable lasers in the UV range can be obtained by frequency multiplication.
However, the prior art spectrometers require an expensive technique and are expensive because of the high output requirement of the laser beams used, they require much energy, and they are not readily portable.